Remembering Enrico Fermi

Report on Forum-Sponsored Session: 2010 'April' Meeting

By Gloria B. Lubkin, Forum Past Chair

Enrico Fermi in the classroom, date unknown.
Photo by Samuel Goudsmit, courtesy of Emilio Segrè Visual Archive, Goudsmit Collection.

Enrico Fermi in the classroom, date unknown.

Fermi with Maria Goeppert-Mayer
Photo courtesy of AIP Emilio Segrè Visual Archive, Goudsmit Collection.

Fermi with Maria Goeppert-Mayer.

Enrico Fermi
Photo by Samuel Goudsmit, courtesy of Emilio Segrè Visual Archive.

Enrico Fermi.

An invited FHP session called "Remembering Enrico Fermi," organized and chaired by James Cronin (University of Chicago), was a highlight of the joint APS-AAPT meet­ing in Washington in mid-February (the "April" meeting). The audience of several hundred, in the largest room available at the meeting, appeared touched by the reminiscences of the three speakers, all of whom worked for Fermi at Chicago. Cronin was a graduate student at Chicago 1951-55. He edited a book that grew out of a 2001 Chicago meeting commemorating the hundredth anniversary of Fermi's birth, Fermi Remembered (University of Chicago Press, 2004). In his intro­ductory remarks at the session, Cro­nin said that when Fermi moved to Chicago immediately after the end of World War II, his passion was to reach the highest energy possible. The mid-1950s began the golden age of particle physics.

The first talk, by T. D. Lee (Colum­bia University), was called "Fermi at Columbia and Reminiscence of Chica­go Days." Lee said that when the first anti-Semitic law was passed in Fascist Italy in 1938, Fermi wrote to George Pegram, then chair of the Columbia physics department. Fermi reminded Pegram that when they had met a couple of years earlier, Pegram asked if Fermi would be interested in coming to Columbia. When Pegram promptly offered him a job, Fermi cabled his acceptance. Then Fermi wrote again to ask if Pegram knew of any job opportunities in the US for other out­standing young Italian physicists, and mentioned Emilio Segrè (who was in Berkeley on a fellowship); Bruno Rossi, Guilio Racah, Ugo Fano, and Franco Rasetti. Fermi described each person's expertise, marital status, and number of children. Fermi was "very humane," Lee said. "His foremost worries were about his colleagues and their survival if they remained in Italy."

That December Fermi and his fam­ily left Italy for Stockholm, where he received the 1938 Nobel Prize for Physics. Instead of returning to Italy, the Fermis arrived in New York on 2 January 1939. When Niels Bohr arrived in New York two weeks later, Laura and Enrico Fermi met him at the dock. Although Bohr had been told by Otto Frisch about the experiments of Otto Hahn and Fritz Strassmann, the theory of fission by Frisch and Lise Meitner, and Frisch's experimental confirmation, Bohr did not mention the remarkable discovery to Fermi. On 20 January, Lee said, Willis Lamb returned from Princ­eton, where he had just learned of the fission discovery from Bohr. It was a Saturday morning and the Pupin Phys­ics Lab was deserted, but Lamb was eager to spread the big news. Fermi arrived after lunch, and Lamb told him. Fermi quickly disappeared to his lab, realizing that there was a much easier way to observe fission. On 25 January, Fermi and several colleagues succeeded.

After World War II, in 1946, Fermi moved to Chicago. That same year Lee arrived from China on a fellow­ship. "One of the most precious events in Chicago was in 1948 when Maria Goeppert-Mayer gave an interesting but somewhat confused talk on levels of different nuclei and why there were some mysterious stability numbers." At the end of her talk, Fermi said, "'Is there any indication of spin-orbit cou­pling?' The bell rang and that was the end of the seminar." A few weeks later she gave a second seminar, "and that was the shell model." At this second seminar Lee initially thought, " 'No, not again,' because the first [seminar] was totally confusing. But the second seminar was totally different. Maria started with Fermi's question and the magic numbers worked out magically. This then led to the 1963 Nobel Prize in Physics."

Fermi once asked Lee the approxi­mate temperature of the Sun at its cen­ter. Lee replied, "Ten million degrees." Fermi asked "How do you know?" Lee told him he had looked it up. Fermi asked if he'd verified the number and Lee replied, "It's really compli­cated. It's not so easy to integrate these equations." Fermi suggested that Lee build a huge specialized slide rule that would enable the solution of two radiative transfer equations, one that involved the 18th power of the tem­perature, and the other that involved the reciprocal of temperature to the 6.5th power. Over the next few weeks Lee built a slide rule that was 6.7 feet long, and carried out the necessary integration. "It was great fun," he said.

The second talk was by Richard Garwin (IBM Research Labs), whose topic was "Working with Fermi at Chi­cago and Los Alamos." Garwin came to Chicago in 1947. After a few months of course work he got up the courage to ask Fermi if he could help in Fer­mi's lab. Fermi had a machine shop in his lab, including a lathe and a cutting saw. Although he had great respect for the technicians in the central machine shop, he felt they were too fastidious, and would take ten times as long to make something ten times more accu­rate than was needed. When the new Chicago cyclotron started working the beams needed to be extracted and targets positioned. In the cyclotron, rather than having the targets mounted on probes, Fermi devised a trolley cart that moved along the cyclotron rim. The cart carried a small copper or car­bon target that could be flipped into and out of the beam.

Garwin recalled, "Among my regrets is one already cited by T. D. When I joined the faculty in 1949 after I got my PhD, I was given my own laboratory at the Institute of Nuclear Studies." Garwin was busy doing experiments on the betatron and plan­ning experiments for the cyclotron. "One day Fermi came in (I'd missed the seminar) and in typical fashion asked if I'd thought about including spin-orbit interactions in the calculation of wave functions and energy levels. So I thought about that." Two weeks later Fermi came in and asked Garwin if he had made any progress on the idea and Garwin said, "None. So he said he'd talk to Maria Mayer about it. I'd simply lacked the courage to put down what I was doing, pick up a new chal­lenge, where, in fact, I would not have done as well as Maria."

Because Chicago paid faculty sala­ries only nine months in a year, Fermi suggested that Garwin consult for Los Alamos in the summer. Fermi had gone to Los Alamos in Fall 1944 and worked there through 1945. "He wasn't in charge of any development group, although there was an F group named for Fermi. He was a treasured consultant known as 'the Pope.'" If anyone needed to know the answer to a calculation he'd show them how to do it, "or in extremis, provide an answer." During the summer of 1950 Garwin shared an office with Fermi, where people would come to talk to him.

One visitor was Frederick Reines, who suggested that with all the explo­sions taking place at the Nevada Test Site, he could put a detector under­ground and detect antineutrinos from the beta decay of fission products. A 17-kiloton nuclear weapon would be made with a few kilograms of uranium and yield neutrinos only from fission products. Fermi responded that it would be preferable to use one of the modern reactors that burned several kilograms of uranium each day. "So Fermi's suggestion led Reines to do the more feasible experiment—at a reactor—for which Fred received the Nobel Prize in 1995."

At Los Alamos Fermi was con­cerned with many things, includ­ing the Taylor instability. "It's a very important phenomenon in nuclear weaponry and other fields," Garwin said. Fermi tried a two-dimensional model, in which a broad tongue of fluid moves into dense material and a narrow tongue moves in the opposite direction and falls. He solved the prob­lem numerically but wasn't satisfied with the solution. One afternoon, John von Neumann came by, saw Fermi and asked what he was doing. Von Neumann returned fifteen minutes later and wrote on the blackboard how to approach the problem analytically. Fermi leaned against his doorpost and said, "That man makes me feel I know no mathematics at all."

"Fermi used to say he could solve only six problems, but he was very good at transforming any other prob­lem into one of those six." His crude approach found the narrow tongue proceeding into vacuum with a large amplitude and uniform acceleration at 8/7 g. In the more rigorous analytical calculation that he did with von Neu­mann, the limiting acceleration was still 8/7 g. "Fermi had it very right."

Back at Chicago, Garwin recalled, Edward Teller (a Chicago faculty mem­ber) dropped by with his latest enthu­siasm. Fermi remarked, "That's the only monomaniac I know with more than one mania."

The Fermi memorial session's last speaker was Fermi's last graduate student—Jerome Friedman (MIT), whose title was "A Student's View of Fermi." Friedman recalled that when he entered the University of Chicago in 1950, "I had no credentials in phys­ics." During his short time in Chicago, Friedman said, Fermi led the group that discovered the so-called (3,3) reso­nance, which has isotopic spin 3/2 and spin 3/2. Fermi did not jump to con­clusions, and "it took him some time to accept its validity. It was the first indication of substructure in the nucle­on." His work also served to confirm charge symmetry and isotopic spin conservation in the strong interaction.

When Friedman passed the PhD exam, he summoned all his courage and asked Fermi if he could do his PhD research under Fermi's supervi­sion. "He said, 'Yes.' I was overjoyed, and he didn't even ask about my qualifications." On a few occasions Friedman was invited to parties at the Fermi home. "His students were his extended family. Often there were parlor games; he was very competitive and clearly liked to win."

"Fermi was a cheerful man with a good sense of humor," Friedman said. Fermi enjoyed the annual Christmas party where the students poked fun at senior faculty members. Valentine Telegdi, then a junior faculty member, "had an uncanny ability to imitate some of the stellar figures in phys­ics. At one Christmas party Val was enclosed in a huge box with flashing lights that represented a computer. It was named the Enriac or Fermiac; I don't remember which. Fermi's voice emanated from the box in a very slow, authoritative manner. This computer was supposed to answer any order of magnitude question and did so. Fermi was clearly amused."

At Chicago many speakers visited. Fermi would inevitably have many comments and questions. "His ques­tions were gentle but sometimes dev­astating to the speaker. They usually started off with, 'There is something I do not understand.' And then it was a problem for the speaker."

In the summer of 1954 Fermi went to Italy, where he became ill. When he returned to Chicago in Septem­ber, he and Friedman waved to each other in the corridor. "I was struck by how gaunt he looked." The next day Fermi had exploratory surgery and was found to have inoperable cancer. Subrahmanyan Chandrasekhar told Friedman that when he and Herbert Anderson visited Fermi at the hos­pital, they were initially at a loss for words. Fermi sensed their difficulty and put them at ease by asking, "Tell me, Chandra. When I die, will I come back as an elephant?" After that the conversation went smoothly.

After Fermi's death on 28 Novem­ber 1954, Friedman was asked to gather together the things in his men­tor's office. "I found only about four books, and one was by his boyhood friend, Enrico Persico. It was clear Fermi didn't need books. He worked out everything for himself. Over half a century later I still look back in awe at this great physicist and remarkable human being."

Note Added: This article represents the views of the author, which are not necessarily those of the FHP or APS.